924 



THE OROAXS OF RESPIRATIOX 



l)i-()nclius is ))lacc'(l lu'xt. and tlir upper vein is again tlic lowest. From before 

 backwards on both sides, the arrangement is — upi)er vein, artery, and bronehus. 



The weight of the lungs together is about forty-two ounces; the right lung is 

 about two ounces heavier than the left. 



In color the lungs are of a i)inkish white; but they become darker, mottled, 

 and even black, as age advances. 



Structure. — The lungs possess an external serous coat derived from the 

 pleura, beneath which is a delicate subserous layer. 



The parenchyma, or lung substance, is comjmsed of minute lobules con- 



FiG. 545. — Anterior View of the Luxos: PERiCARmrM. (Moditied IVoni Bourgery.] 



Vaia cai a svpei toi 



BRONCHUS 

 Puhnonai y ailfiy 

 Pulmonai ii lein 



A)fli 01 aotia 



Puhiii»iai >i ntlfry 

 BRONCHUS 

 Puhnonat y vein 



ENSIFORM CARTILAGE 



nected by interlobular areolar tissue. Each lobule is made up of a ramification of 

 a bronchial tube with its cluster of terminal air cells, with a minute plexus of 

 pulmonary and bronchial vessels, nerves, and lymphatics. 



The vessels. — The pulmonary arteries convey venous blood from the heart 

 to the lungs; they divide into bvaneln^s wliich follow the bronchial tubes, and 

 finally terminate in a flat mesln\H)rk upon the walls of the intercellular passages 

 and air cells. 



The radicles of the pulmonary veins start from this network; they coalesce 

 into larger brandies wliieb aceompany the artei'ies and terminate in two large ves- 

 sels on each side, wliieb retui-n tbe arterial blood to the left auricle of the heart. 



